Extensive pipeline systems exist for carrying gas or liquid under pressure over long distances. These pipelines are subject to corrosion and, under certain conditions, are subject to failure by the generation of a crack running in the axial direction of the pipeline at high speeds and with tremendous force. Over the years, methods have been developed for repairing corroded portions of a pipeline and for limiting ductile and brittle fracture propagation in such pipelines. One such method involves the application of a coiled band of a high tensile strength composite material around the pipeline. Methods employing these composite bands for repairing and reinforcing a pipeline are described in published Canadian Patent Application No. 2,028,524, and methods employing these composite bands as a crack arrester to limit ductile fracture propagation in a pipeline are described in U.S. Pat. No. 4,700,752. The disclosures of both of these documents are incorporated by reference herein.
The composite bands employed in the above-noted methods consist of continuous fibers of a high tensile strength material encapsulated in a resin matrix. The processes utilized heretofore for manufacturing these composite bands have suffered from various drawbacks. In one such process, the high tensile strength fibers were provided in the form of a tape having multiple cross threads holding the fibers together, the cross threads being held in place by strips of a hot-melt glue. One difficulty associated with the use of such tapes has been an inability to consistently surround and encapsulate the fibers with a resin coating. Another problem with processes employing these tapes is that the heat associated with the gelling and curing of the resin causes the strips of hot-melt glue to melt, leaving voids which extend across the composite band. These voids act as channels enabling water to penetrate and attack the fibers, thereby causing the bands to weaken over time.
In order to overcome some of these difficulties, the inventors herein have experimented with processes employing individual fibers which are not connected by cross threads. The experimental processes employing individual fibers which have been attempted heretofore, however, have produced bands having undulating inner and outer surfaces. That is, tension in the continuous fibers during the manufacturing process has caused these bands to have a random series of peaks and valleys which extend on each surface in the length direction of the band. The peaks and valleys on adjacent convolutions of the composite band interfere with one another when it is desired to radially align the convolutions during installation, thereby making the installation process more difficult.
Another problem associated with these experimental composite bands relates to the intended function of the band as a reinforcement for structures. Typically, during the installation of composite bands around, for example, pipelines, an adhesive is applied between adjacent convolutions of the band as the band is wound around the pipeline. This adhesive is intended to keep the band from uncoiling under the very high fluid pressures at which these pipelines normally operate. However, some problems relating to the use of these adhesives have been experienced as these bands have been installed on simulated pipelines for testing purposes. These problems include difficulties in developing adequate adhesive strength between adjacent convolutions of the band on a consistent basis and in achieving a sufficiently rapid and consistent adhesive cure rate. A further problem has been an inability to obtain very thin and uniform layers of adhesive to minimize "cushioning" affects caused by the adhesive layers between adjacent convolutions of the band.
There therefore exists a need for improved processes for fabricating high tensile strength composite bands incorporating continuous high tensile strength fibers in a resin matrix. There further exists a need for methods for regularly developing strong adhesive bonds between adjacent convolutions of these bands as the bands are installed to reinforce a structure.